1. Field of the Invention
The present invention relates to a sheet ejection device used for a copier, a printer, a facsimile, a multifunction peripheral thereof, and the like, and an image forming apparatus and a post-processing apparatus that are provided therewith. In particular, the present invention relates to a sheet ejection device including an ejection roller pair, and an image forming apparatus and a post-processing apparatus that are provided therewith.
2. Description of the Related Art
The image forming apparatus includes the ejection roller pair for ejecting a sheet on which an image is formed by an image forming portion. The sheet transported from an upstream side of the ejection roller pair is ejected onto an ejection tray by the ejection roller pair. When the ejection roller pair sends out the sheet to the ejection tray, there may be a malfunction that a back end of the sheet is apt to remain on a lower roller of the ejection roller pair. In order to solve this malfunction, there is a structure in which the lower roller of the ejection roller pair is provided with protrusions so that the back end of the sheet is pushed out to the ejection tray by the protrusions.
For instance, in a sheet ejection device described in Patent Document 1, the ejection roller pair is constituted of a lower roller and an upper roller sandwiching a nip. The lower roller is provided with a roller main body forming the nip, and a plurality of protrusions for pushing the back end of the sheet to be ejected are disposed on both ends of the roller main body in the circumferential direction. Each of the protrusions protrudes in a radial direction from an outer circumference surface of the roller main body. Thus, when there is a possibility that the back end of the sheet ejected by the ejection roller pair remains on the lower roller, the protrusions can push out the back end of the sheet so that the remaining of the back end of the sheet is prevented.
In addition, in a sheet ejection device described in Patent Document 2, the ejection roller pair is constituted of a lower roller and an upper roller sandwiching a nip. Flanges having a larger diameter than the lower roller are disposed on both ends of the lower roller. A plurality of protrusions are disposed on a circumference surface of the flange. When the lower roller rotates in a positive direction so as to eject the sheet, an end on a kick out side of the protrusion engages with the back end of the sheet so as to provide a kick out force. When the lower roller rotates in an opposite direction to switch back the sheet, because an end on a reverse feed side of the protrusion has a gentle slope, a kick out mark is not formed on the sheet due to the reverse rotation of the lower roller.
In addition, a sheet ejection device described in Patent Document 3, the ejection roller pair is constituted of a lower roller and an upper roller sandwiching a nip. A protrusion is formed on the outer periphery of the lower roller. When the lower roller rotates, the protrusion acts to push out the back end of the sheet to the ejection tray side.